Conventional Film and paper Drying in the photo processing trade is typically done by moving the web on a series of rollers through a heated chamber. A fan or blower is used to move air over a resistance heater, around the film and out of the processor into the surrounding work area. Higher volume units use an impingement jet dryer in which a blower pressurizes a plenum with heated air. Slots cut into the plenum allow streams of air to blow against the surface of the film. These slots are typically an inch or so from the film to allow the stream to spread over the surface of the film. In both cases large amounts of costly heated air must be vented to the environment, heating the surrounding room. In addition, heated air escapes within the processor, heating the processor solutions.
The above inefficiencies are the result of conventional film (or paper) processing devices not providing a sufficient level of agitation at the film-air interface. As a result, a region of reduced temperature, is created in the layer of air which exists at the film surface during the drying process of the processor. This layer is the thermal boundary layer.
Analysis and experimental measurements of conventional dryers indicate that boundary layers exist which are thick enough so as to become the drying rate limiting parameter. More specifically, the transfer of chemical mass and heat energy through the thermal boundary layer occurs more slowly than transfer through the film itself. This condition results in low drying speeds, excessively long film paths and increased size of the dryer. Drying temperatures need to be excessively high to maintain reasonable film drying rates resulting in inefficient utilization of thermal energy.